Halation has been a persistent problem with photographic films formed by depositing one or more layers of a photosensitive silver halide emulsion onto a support such as a plastic film. The emulsion diffusely transmits light. Such light reaches the support and is reflected back into the emulsion. The silver halide emulsion is thereby reexposed at a location different from the original one. The result is a halo surrounding an image of a bright object on the film.
Efforts to minimize the effects of halation have included incorporation of silver or silver halide in the support to lower reflection density (see U.K. Patent No. 1,126,797). U.S. Pat. No. 4,460,679 approaches the problem by adding a non-photosensitive layer containing a chemically bleachable, high strength tinctorial colorant, such as blue colloidal silver, over the support which permits sensitometric control over low coating weight silver halide elements. U.S. Pat. No. 4,563,406 discloses a yellow, blue or gray colorant layer, a white pigment layer and a silver halide emulsion layer over the support to achieve the combined effect of increased sharpness without loss of sensitivity.
U.S. Pat. No. 2,921,914 uses a blue colloidal silver dispersion to absorb longer wavelengths of light for halation control. Preparation of this dispersion involves spontaneous nucleation to derive centers for silver formation, and reduction of the silver salt by tannic acid in the presence of a water soluble strontium salt. This technique has hue control problems related to large nuclei, turbidity and difficulties with bleaching. Severe gel slugging (forming hardened globs), a major concern in antihalation silver preparation, is aggravated by the use of tannic acid.
U.S. Pat. Nos. 5,246,823 and 5,318,885 disclose photographic elements including a reflective support, one or more photosensitive silver halide emulsion layers, and a colored antihalation layer interposed between the support and the photosensitive layers. The antihalation layer comprises platelets of silver having a thickness of up to about 20 nanometers (nm) distributed in a suitable matrix or colloidal medium such as gelatin. Due to the thinness of the grains, coverage of up to about 10 mg silver per square foot of the antihalation layer provides a sufficient antihalation effect at reduced silver levels as compared to silver antihalation layers containing larger, thicker grains.
Very often carbon black is used in dispersed form in a binder. A carbon black antihalation layer provides excellent halation protection and has excellent antistatic properties. U.S. Pat. No. 4,990,434 discloses photographic elements comprising an alkali-soluble carbon black antihalation layer on a subbed hydrophobic transparent polyester film support, said subbing layer being adapted to improve the adhesion of said antihalation layer to said subbed film support and at the same time to improve the removability in alkaline solution of said antihalation layer from said subbed film support.
In silver halide photographic materials, aqueous alkaline soluble antihalation layers containing carbon black are used on the backside of the photographic media. These antihalation layers are dissolved and removed during development of the photographic media. Such antihalation layers are shown in U.S. Pat. Nos. 2,271,234; 3,392,022; 4,039,333 and 4,262,088.
The use of bleachable dye-containing layers as antihalation layers is also known in the art. The dyes may be chemically bleachable (e.g., U.S. Pat. Nos. 3,769,019 and 4,336,323) or heat bleachable (e.g., U.S. Pat. Nos. 4,196,002 and 4,316,984).
Each of these systems provide improved halation characteristics to the imaging media, but also provide some additional problems. A particular problem is the poor coating quality; in fact, streaks are generated on the photographic material. Very often, irregularities on the film support base determine a poor quality of the photographic material because the same irregularities of the support base are transferred to the photographic element which is coated overthere. The result is the presence of mottles or streaks.
Photographic material is conventionally constructed as a multilayered element including an electrically insulating support and photographic light-sensitive emulsion layers. This photographic material is susceptible to accumulation of electrostatic charges caused by repeated frictional contacts between the photographic material with surfaces of the same or different kinds of materials, or during peeling operations performed in order to separate superposed materials of the same or different kinds during the manufacture of, or use of, the photographic material. These accumulated electrostatic charges can cause many problems. The most serious problem being that the light-sensitive emulsion layers can be inadvertently sensitized by the discharge of these accumulated electrostatic charges before development processing is performed which results in the generation of dot-like spots, or dendritic or feather-like streaks in the development processed photographic film. These spots and streaks are generally called static marks, and considerably diminish, if not destroy, the commercial value of the photographic film.
It is also known to protect photographic elements against mechanical damage by coating them with a layer comprising a wax. This wax serves as a lubricant and for that reason tends to reduce the formation of scratch markings. However, some lubricants have a deleterious effect on the photosensitive silver halide emulsion, whilst others streak the film surface, thus spoiling the quality of the final image obtained.